Nowt wrong with a decent MK4.
My dad has had one from brand new, only thing is he bought a crappy 2.0 and that engine was nothing nut problems.
Iv since installed a 180 bhp 20vt and 6 speed gearbox from a Anniversary model.
The Mk4s rust as bad as any mk3, (and they are alot newer) arches where the plastic liner rubs against it and also the tailgate around the handle are problem areas. subframes rust like a mofo on all cars we have worked on - you dont get this as bad on any mk3 we worked on so far..
They handle like a sofa in standard foMr too. much more boat like than a Mk3 but i guess mud sticks

In a nutshell, they are not bad cars, prefer my Mk3 over any mk4 tho, but its hardly a normal mk3 that I drive... that said its never once give me any hassle in 5 years even with the old crap 8v lump.. been a great car, its built solid and no rust..
If i was to start over, and was not going to change engines etc, Id prob rather have the Turbo mk4 over a 16v or VR6 powered mk3...